The present invention relates to filters, and more particularly to etched disc stack filter elements and filter assemblies including such filter elements.
In order to remove solid particles from a flowing gas or liquid, wire mesh or sintered filters have heretofore been used, particularly for the separation of particles smaller than 100 microns. Such filters may have certain advantages when compared to an etched disc filter element comprised of a stack of filter discs. In a wire mesh screen, for example, each flow passage through the screen is very short thus minimizing pressure drop through the filter. Additionally, wire mesh screen may be advantageous in maximizing the ratio of open or pore area relative to the solid area of the filter mesh and thus provide a greater filter capacity per unit weight of the structure. However, wire mesh and sintered filters inherently have certain disadvantages. For example, it is virtually impossible to attain uniform size of pores or interstices in a wire mesh or sintered filter; the filters have an inherently low resistance to high pressure differentials; and the filter elements cannot be satisfactorily back-flushed for cleaning and re-use.
Stacked sheet filters, such as that disclosed in U.S. Pat. No. 3,648,843 to Pearson, overcome many of the disadvantages of wire mesh and sintered filters. However, as compared to wire mesh and sintered filters, stacked sheet filters typically have relatively long flow passages therethrough and, accordingly, induce a relatively high pressure drop. Further, stacked sheet filters have a relatively low ratio of open space to closed space as compared to wire mesh and sintered filters.
Current etched disc filter elements utilize a multitude of individual discs with a round or modified round configuration stacked one on top of the other. The basic flow path of media in these existing systems is from the outside diameter of a disc to the interior region of a disc. Therefore, the diameter of the discs and/or the overall length of the disc stack must be increased to produce a larger filter area. Creating a larger filter area by increasing the diameter of each disc or the overall length of the disc stack increases the size, weight, cost and complexity of the filter element. Although the direction of the flow of media is normally from the outside diameter to the interior region of the discs, there are times when a reversal of the flow direction is needed, such as to clean the filter element. Based on existing filter element architecture, this results in a decrease in the overall efficiency of the filter element since the inlet and outlet flow passages are unequal in size.
The present invention relates to a etched disc stack filter element and assembly. In embodiments of the present invention, discs in the disc stack have filtering arms on which are etched flow channels. These filtering arms separate inlet and outlet flow passages. As the medium to be filtered flows from an inlet passage to an outlet passage, contaminants too large to pass through the etched flow channels are removed or separated from the medium.